Apparatus, method, and system for diagnosing reductant deposits in an exhaust aftertreatment system

ABSTRACT

An exhaust gas treatment system for an internal combustion engine may have a reductant delivery system that delivers reductant to an exhaust stream in an exhaust aftertreatment system. A temperature sensor may be positioned in or near the flow of reductant and exhaust to measure the temperature of the reductant and exhaust. A change in temperature over time, such as an increase, decrease, or change in variation amplitude, may indicate the presence of a reductant deposit in the system. Detection of the deposit may initiate a regeneration cycle in which the operating characteristics of the system change to eliminate the reductant deposit to prevent it from hindering the performance of the exhaust aftertreatment system.

FIELD

This disclosure relates to internal combustion engines, and moreparticularly to diagnosing the operation of a reductant delivery systemfor treating exhaust gas in an exhaust gas aftertreatment system.

BACKGROUND

Emissions regulations for internal combustion engines have become morestringent over recent years. Environmental concerns have motivated theimplementation of stricter emission requirements for internal combustionengines throughout much of the world. Governmental agencies, such as theEnvironmental Protection Agency (EPA) in the United States, carefullymonitor the emission quality of engines and set acceptable emissionstandards, to which all engines must comply. Consequently, the use ofexhaust aftertreatment systems on engines to reduce emissions isincreasing.

Generally, emission requirements vary according to engine type. Emissiontests for compression-ignition (e.g., diesel) engines typically monitorthe release of carbon monoxide (CO), unburned hydrocarbons (UHC), dieselparticulate matter (PM) such as ash and soot, and nitrogen oxides(NO_(x)).

With regard to reducing NO_(x) emissions, NO_(x) reduction catalysts,including selective catalytic reduction (SCR) systems, are utilized toconvert NO_(x) (NO and NO₂ in some fraction) to N₂ and other compounds.SCR systems utilize a reductant, typically ammonia, to reduce theNO_(x). Currently available SCR systems can produce high NO_(x)conversion rates allowing the combustion technologies to focus on powerand efficiency. However, currently available SCR systems also sufferfrom a few drawbacks.

SCR systems utilize a reductant delivery system to introduce areductant, such as aqueous urea or diesel exhaust fluid, into theexhaust stream upstream of the SCR catalyst. The reductant may tend toform deposits over time within the exhaust aftertreatment system, suchas on exhaust aftertreatment components (e.g., reductant dosers) and/oron the walls of exhaust conduits (e.g., reductant decompositionchambers). Such deposits can adversely affect the operation of theengine (e.g., by restricting the exhaust flow passageway) and theexhaust aftertreatment system (e.g., by impeding the catalyticreaction). If the deposit is not soon detected and remedied, the enginesystem may not function properly. For example, reductant deposits maynegatively affect fuel consumption, NO_(x) reduction efficiency, andother operating characteristics of an internal combustion engine.

SUMMARY

The subject matter of the present application has been developed inresponse to the present state of the art, and in particular, in responseto the problems and needs in the art that have not yet been fully solvedby currently available exhaust aftertreatment systems. Accordingly, thesubject matter of the present application has been developed to provideapparatus, methods, and systems for diagnosing reductant deposit buildupthat overcome at least some shortcomings of the prior art exhaustaftertreatment systems.

According to one embodiment, an apparatus for diagnosing existence ofreductant deposits in an exhaust aftertreatment system may have areductant delivery system that delivers reductant to exhaust gasproduced by an internal combustion engine to provide a mixture ofexhaust gas and reductant, and a control module that operates thereductant delivery system. The apparatus may further have a samplingmodule that samples a first temperature of the mixture of exhaust gasand reductant and samples a second temperature of the mixture of exhaustgas and reductant, a calculation module that calculates a temperaturedifferential between the first and second temperatures, and a comparisonmodule that compares the first pressure differential with a thresholdtemperature differential to determine whether a reductant deposit existswithin the exhaust aftertreatment system.

Such an apparatus may further have a reporting module that reports aperformance status indicating existence of a reductant deposit withinthe exhaust aftertreatment system.

Such an apparatus may further have a regeneration module that receivesthe performance status and, in response to receipt of the performancestatus, initiates a regeneration cycle of the exhaust aftertreatmentsystem to at least partially remove the reductant deposit.

In such an apparatus, the sampling module may obtain the first andsecond temperatures from a temperature sensor positioned in a boss thatextends from a decomposition chamber of the exhaust aftertreatmentsystem, wherein the reductant delivery system delivers the reductant tothe exhaust gas through the boss.

In such an apparatus, the sampling module may obtain the first andsecond temperatures from a temperature sensor positioned in or near theexhaust aftertreatment system. After sampling the first temperature, thesampling module may wait for a time increment sufficient for thereductant deposit to form or increase significantly in size aftersampling the first temperature.

In such an apparatus, the threshold temperature differential may be atemperature rise from the first temperature to the second temperature.The comparison module may determine that the reductant deposit exists ifthe second temperature exceeds the first temperature by an amountgreater than the temperature rise.

In such an apparatus, the threshold temperature differential may be atemperature drop from the first temperature to the second temperature.The comparison module may determine that the reductant deposit exists ifthe first temperature exceeds the second temperature by an amountgreater than the temperature drop.

In such an apparatus, the threshold temperature differential may be amagnitude of temperature variation. The comparison module may determinethat the reductant deposit exists if the absolute value of thedifference between the first and second temperatures is greater than themagnitude of temperature variation.

In such an apparatus the sampling module may further takes a pluralityof temperature samples to obtain at least one of the first and secondtemperatures. At least one of the first and second temperatures may bean average temperature of the plurality of temperature samples.

According to one method for diagnosing existence of a reductant depositin an exhaust aftertreatment system, the exhaust aftertreatment systemmay deliver reductant to exhaust gas produced by an internal combustionengine to provide a mixture of exhaust gas and reductant. The method mayinclude positioning a temperature sensor in or near the exhaustaftertreatment system, sampling a first temperature of the mixture ofexhaust gas and reductant with the temperature sensor, and using thefirst temperature to make a comparison to determine whether a reductantdeposit has formed in the exhaust aftertreatment system.

Such a method may further include reporting a performance status thatthe reductant deposit exists within the exhaust aftertreatment system,and initiating a regeneration cycle of the internal combustion engine toat least partially remove the reductant deposit in response to receiptof the performance status.

Such a method may further include waiting for a time incrementsufficient for the reductant deposit to form or increase significantlyin size after sampling the first temperature, sampling a secondtemperature of the mixture of exhaust gas and reductant with thetemperature sensor after waiting for the time increment, and calculatinga temperature differential between the first and second temperatures.

In such a method, the temperature sensor may be positioned in a bossthat extends from a decomposition chamber of the exhaust aftertreatmentsystem. Delivering reductant to the exhaust gas may include deliveringthe reductant through the boss.

In such a method, the threshold temperature differential may be atemperature rise from the first temperature to the second temperature.Comparing the temperature differential with the threshold temperaturedifferential may include determining that the reductant deposit existsif the second temperature deposit exists by an amount greater than thetemperature rise.

In such a method, the threshold temperature differential may be atemperature drop occurring from the first temperature to the secondtemperature. Comparing the temperature differential with the thresholdtemperature differential may include determining that the reductantdeposit exists if first temperature exceeds the second temperature by anamount greater than the temperature drop.

In such a method, the threshold temperature may be a magnitude oftemperature variation. Comparing the temperature differential with athreshold temperature differential may include determining that thereductant deposit exists if the absolute value of the difference betweenthe first and second temperatures is greater than the magnitude oftemperature variation.

In such a method, at least one of sampling the first temperature andsampling the second temperature may include taking a plurality oftemperature samples. At least one of the first temperature and thesecond temperature may be an average temperature of the plurality oftemperature samples.

An internal combustion engine system may have an internal combustionengine, an exhaust aftertreatment system in exhaust gas receivingcommunication with the internal combustion engine, a reductant deliverysystem in reductant supplying communication with exhaust gas in theexhaust aftertreatment system to provide a mixture of exhaust gas andreductant, a temperature sensor positioned to measure temperature of themixture of exhaust gas and reductant, and an on-board diagnostic systemthat samples temperature data from the temperature sensor and uses thetemperature data to determine whether a reductant deposit exists withinthe exhaust aftertreatment system.

In such an internal combustion engine system, sampling temperature datafrom the temperature sensor may include obtaining a first temperatureand a second temperature from the temperature sensor. The on-boarddiagnostic may further calculate a temperature differential between thefirst and second temperatures to provide a first temperaturedifferential, and may compare the first temperature differential with athreshold temperature differential to determine whether a reductantdeposit has formed in the exhaust aftertreatment system.

In such an internal combustion engine system, the temperature sensor maybe positioned in a boss that extends from a decomposition chamber of theexhaust aftertreatment system. The reductant delivery system may deliverthe reductant to the exhaust gas through the boss.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the subject matter of the present disclosureshould be or are in any single embodiment. Rather, language referring tothe features and advantages is understood to mean that a specificfeature, advantage, or characteristic described in connection with anembodiment is included in at least one embodiment of the presentdisclosure. Thus, discussion of the features and advantages, and similarlanguage, throughout this specification may, but do not necessarily,refer to the same embodiment.

The described features, structures, advantages, and/or characteristicsof the subject matter of the present disclosure may be combined in anysuitable manner in one or more embodiments and/or implementations. Inthe following description, numerous specific details are provided toimpart a thorough understanding of embodiments of the subject matter ofthe present disclosure. One skilled in the relevant art will recognizethat the subject matter of the present disclosure may be practicedwithout one or more of the specific features, details, components,materials, and/or methods of a particular embodiment or implementation.In other instances, additional features and advantages may be recognizedin certain embodiments and/or implementations that may not be present inall embodiments or implementations. Further, in some instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the subject matter ofthe present disclosure. The features and advantages of the subjectmatter of the present disclosure will become more fully apparent fromthe following description and appended claims, or may be learned by thepractice of the subject matter as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the subject matter may be more readilyunderstood, a more particular description of the subject matter brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the subject matter and arenot therefore to be considered to be limiting of its scope, the subjectmatter will be described and explained with additional specificity anddetail through the use of the drawings, in which:

FIG. 1 is a schematic diagram of an internal combustion engine systemhaving an internal combustion engine and a reductant delivery system inaccordance with one representative embodiment;

FIG. 2 is a schematic block diagram of the on-board diagnostic systemand controller of the internal combustion engine system of FIG. 1according to one embodiment;

FIG. 3 is a cross-sectional side elevation view of a reductant doserboss and reaction chamber of an exhaust aftertreatment system accordingto one embodiment;

FIG. 4 is a chart illustrating how temperature data may change over timeas a reductant deposit builds in an exhaust aftertreatment systemaccording to one embodiment; and

FIG. 5 is a flow chart diagram illustrating a method for diagnosingand/or responding to the existence of a reductant deposit in an exhaustaftertreatment system according to one embodiment.

DETAILED DESCRIPTION

FIG. 1 depicts one embodiment of an internal combustion engine system10. The main components of the system 10 include an internal combustionengine 20 and an exhaust gas aftertreatment system, which may include aselective catalytic reduction (SCR) system 18. The SCR system 18includes a decomposition or reaction chamber 22 in which the catalyticprocess may occur. The reaction chamber 22 may be in exhaust gasreceiving communication with the internal combustion engine 20 via anexhaust line 24. The reaction chamber 22 can include any of variouscatalysts, such as an SCR catalyst, configured to reduce nitrogen-oxidesin the presence of ammonia, which can be obtained from the reduction ofa reductant, such as aqueous urea.

The internal combustion engine 20 can be a compression-ignited internalcombustion engine, such as a diesel fueled engine, or a spark-ignitedinternal combustion engine, such as a gasoline fueled engine operatedlean. Combustion of the fuel and air in the compression chambers of theinternal combustion engine 20 produces exhaust gas that is operativelyvented to the exhaust line 24. From the exhaust line 24, at least aportion of the exhaust gas stream flows from into and through theexhaust gas aftertreatment system and SCR system 18 prior to beingvented into the atmosphere through a tailpipe 26. A temperature sensor28 may be positioned in or near the exhaust line 24.

Generally, the SCR system 18 may be configured to remove variouschemical compounds and particulate emissions present in the exhaust gasreceived from the exhaust line 24. In addition to the reaction chamber22, the SCR system 18 may include a reductant delivery system 30.Additionally or alternatively, the SCR system 18 may include any ofvarious other exhaust treatment components known in the art, such as anoxidation catalyst, a particulate matter filter, and an ammoniaoxidation catalyst. The reductant delivery system 30 may include areductant source, which may take the form of a reductant tank, areductant pump, and a doser, which operates as a reductant deliverymechanism and may take the form of an injector 36 that injects reductant38 into the exhaust gas stream.

The reductant may be any substance known in the art that facilitates thebreakdown, combination, and/or other conversion to inert form ofpollutants in an exhaust gas stream. Thus, the reductant may includeaqueous ammonia (NH₃), aqueous urea, diesel fuel, diesel exhaust fluid,and/or diesel oil. The injector 36 may be selectively controllable viaactuation of a control valve to inject a desired amount of reductant 38into the exhaust gas stream. The injector 36 may be positioned to injectreductant 38 into the exhaust line 24 upstream of the reaction chamber22 and/or directly into the reaction chamber itself. As will be shown inFIG. 3, the temperature sensor 28 may be positioned proximate theinjection site at which the reductant 38 enters the exhaust stream.

The internal combustion engine system 10 may also include an on-boarddiagnostic system (OBD) system 40 that receives information related tothe operation of the system 10. The OBD system 40 may communicate with acontroller 42 that controls operation of the system 10 and associatedsub-systems, such as the internal combustion engine 20 and the reductantdelivery system 30. The OBD system 40 and the controller 42 are eachdepicted in FIG. 1 as a single physical unit, but each may include twoor more physically separated units or components in some embodiments ifdesired. Alternatively, the OBD system 40 and the controller 42 may becombined into a single unit that performs both diagnostic and controlfunctions.

Generally, the OBD system 40 and the controller 42 may each receivemultiple inputs, process the inputs, and transmit multiple outputs. InFIG. 1, only a few inputs and outputs are shown. More specifically, theOBD system 40 may receive temperature data 50 from the temperaturesensor 28, and may use the temperature data 50 to determine aperformance status 52 of the system 10. More specifically, thetemperature data 50 may be used to determine whether there is areductant deposit residing in the exhaust line 24 and/or the reactionchamber 22. The performance status 52 shown in FIG. 1 may be indicativeof whether such a deposit is present. The performance status 52 mayinclude a number indicative of the size or severity of the deposit, ormay simply include a “yes” or “no” indicator indicating whether thedeposit has reached a threshold size or severity. The OBD system 40 mayissue other performance status data (not shown), which may include dataregarding other operating characteristics of the system 10.

The controller 42 may receive the performance status 52 and/or otherdata and/ based on the performance status 52 and other data, issue acommand 54 to the internal combustion engine 20 and/or issue a command56 to the reductant delivery system 30. The commands 54, 56 may directthe internal combustion engine 20 and/or the reductant delivery system30 to take certain steps to optimize the operation of the system 10(e.g., perform a regeneration of the exhaust aftertreatment system),shut down the system if a safety concern is present, or the like.

If desired, the OBD system 40 and/or the controller 42 may be designedto provide the performance status 52 and/or other data to a user, suchas a driver of the vehicle containing the system 10. The performancestatus 52 may be provided, for example, via a light or LED, an auditorysignal or alarm, an analog gauge, a digital readout, or the like.Moreover, the user may manually select and enter the command 54 and/orthe command 56 based on the performance status 42 indicated to the user.Alternatively, the OBD system 40 and/or the controller 42 may operatesubstantially transparently to the user so that the commands are issuedautomatically.

Referring to FIG. 2, the OBD system 40 and the controller 42 may includevarious modules for diagnosing and controlling the operation of thesystem 10. As shown in FIG. 2, the OBD system 40 may include a samplingmodule 58, a calculation module 60, a comparison module 62, and areporting module 64. The controller 42 may include a control module 66and a regeneration module 68.

While not specifically illustrated and described with reference to FIG.2, the OBD system 40 and/or the controller 42 may include additionalcontroller modules for conducting other control system functions. TheOBD system 40, the controller 42 and/or their various modular componentsmay comprise processor, memory, and interface modules that may befabricated of semiconductor gates on one or more semiconductorsubstrates. Each semiconductor substrate may be packaged in one or moresemiconductor devices mounted on circuit cards. Connections between themodules may be through semiconductor metal layers,substrate-to-substrate wiring, or circuit card traces or wiresconnecting the semiconductor devices.

During normal operation of the reductant delivery system 30, the OBDsystem 40, or more specifically, the sampling module 58, may receivetemperature data 50 from the temperature sensor 28. The sampling module58 may receive other sensor data (not shown) from other sensors thatprovide data regarding the operation of the SCR system 18 such as, forexample, pressure sensor data from the reductant delivery system 30, theexhaust line 24, and/or the reaction chamber 22, temperature data fromother temperature sensors, flow meter data indicating the rate of flowof the reductant 38 into the exhaust stream, and/or data from othersensors as known in the art. However, one benefit of the presentdisclosure is that these sensors may not be required to properlydiagnose whether a reductant deposit exists in the SCR system 18.

The calculation module 60 may use the temperature data 50 and/or othersensor data to calculate metrics useful in diagnosing the operation ofthe SCR system 18, such as temperature differentials occurring over timeas the SCR system 18 operates. The comparison module 62 may compare themetrics provided by the calculation module 60 with other data, such asmetrics obtained from previous operation of the SCR system 18,established thresholds, or the like. The reporting module 64 may, basedon the output of the comparison module 62, provide the performancestatus 52 of the SCR system 18 to, for example, the controller 42. Ifdesired, the performance status 52 may include a variety of data such asflow rates, pressures, temperatures, and other data reflecting theoperating conditions of the SCR system 18.

In certain implementations, the OBD system 40 may accumulate or sum aplurality of errors, or deficiencies, related to exhaust temperatureand/or other aspects of the operation of the SCR system 18 tracked bythe OBD system 40, and compare the accumulated error data with at leastone predetermined threshold. The predetermined threshold can be aregulated threshold or some other threshold associated with a systemhaving an undesirable or unlawful amount of blockage. If the accumulatederror data meets the threshold, then the reporting module 64 may issue aperformance status 52 indicating failure of the SCR system 18 to meetoperational or regulatory standards. However, if the accumulated errordata does not meet the threshold, then the reporting module 64 mayissues a performance status 52 indicating that the SCR system 18“passes,” e.g., the SCR system 18 meets and/or is likely to continuemeeting applicable standards.

Alternatively, the performance status 52 may provide some otherindication (e.g., “poor”) of the performance of the SCR system 18 basedon whether the accumulated error data meets the threshold. Thecomparison module 62 may compare the accumulated error data againstmultiple thresholds to provide a performance status 52 that indicatesone of varying degrees of performance (e.g., “poor, ” “medium-poor, ”“medium, ” “medium-good, ” and “good”). In this manner, the OBD system40 may report to a user the evolution (e.g., rate of decay) of theperformance of the SCR system 18 over time such that a user cananticipate when the SCR system 18 may fail to meet the applicablestandards.

In addition to, or in the alternative to, reporting the performancestatus 52 to the user, the reporting module 64 may provide theperformance status 52 to the controller 42 so that the controller 42 canutilize the performance status 52 to automatically adjust the operationof the system 10. For example, the control module 66 may use theperformance status 52 to issue the command 56 to the reductant deliverysystem 30 to speed up, slow down, or stop the flow of the reductant 38into the exhaust line 24. The regeneration module 68 may use theperformance status 52 to issue the command 54 to the internal combustionengine 20 to modify the operation of the internal combustion engine 20,for example, by initiating a regeneration cycle in which the internalcombustion engine 20 produces exhaust at higher-than-averagetemperatures to burn away or otherwise remove reductant deposits withinthe exhaust line 24 and/or the reaction chamber 22.

Referring to FIG. 3, a side elevation, section view illustrates thejuncture of the exhaust line 24 with the reaction chamber 22, which mayalso be the part of the exhaust line 24 that receives the reductant 38from the reductant delivery system 30. As shown, the exhaust line 24 mayhave an exterior wall 69 defining a generally tubular shape. Thereaction chamber 22 may simply be a region of the generally tubularshape defined by the exterior wall 69 immediately downstream of theentry point of the reductant 38, in which reductant 38 is combined withexhaust 39 to define a mixture in which the catalytic reduction canoccur.

As shown, the exhaust line 24 may have a boss 70 that extends at anangle from the exterior wall 69 of the exhaust line 24. The boss 70 mayhave an aperture 72 through which the reductant 38 is injected by theinjector 36. Thus, the reductant 38 may spray into the exhaust stream asshown (e.g., from left to right in FIG. 3). The regions near orimmediately downstream of the aperture 72, such as within the boss 70,may receive reductant 38 that has not fully mixed with the exhauststream yet, and may thus be particularly susceptible to the buildup ofreductant deposits. However, other locations within the decompositionchamber downstream of the injector 36, such as mixers, walls, and othercomponents, may be susceptible to reductant deposits.

By way of example, a reductant deposit 74A within the boss 70 and areductant deposit 74B on the wall of the reaction chamber 22 downstreamof the boss 70 are illustrated in FIG. 3. Such deposits 74A, 74B aremerely exemplary and need not be located as shown, but deposits may beanywhere in the exhaust line 24, the reaction chamber 22, and/or thetailpipe 26 at or downstream of the entry point of the reductant 38.Additionally, the shapes of the reductant deposits 74A, 74B is merelyexemplary. Reductant deposits may take a variety of shapes, includingstalactite shapes, conical shapes, asymmetrical lumps, etc. Suchreductant deposits may develop on the interior wall of the exterior wall69 or on any structure within the interior of the exhaust line 24, thereaction chamber 22, and/or the tailpipe 26, such as any filters ormixers positioned in any of these locations.

FIG. 3 also illustrates one example of the placement of the temperaturesensors 28A, 28B. As shown, the temperature sensor 28A is within thetrailing end of the boss 70, proximate the location where the trailingend of the boss 70 joins the exhaust line 24. It has been discoveredthat the formation of a reductant deposit like the reductant deposit 74Ain the particular location shown may cause a reduction in thetemperature of the mixture of exhaust and reductant 38 within the boss70 near the temperature sensor 28A. This may be for a variety ofreasons, including the fact that the reductant 38 acts as an insulator,and the flow patterns of exhaust and reductant 38 are altered by thephysical presence of the reductant deposit 74A. Similarly, thetemperature sensor 28B is positioned on a wall of the reaction chambertube downstream of the boss 70. It has been discovered that theformation of a reductant deposit like the reductant deposit 74B in theparticular location shown may cause a reduction in the temperature ofthe mixture of exhaust and reductant 38 within the reaction chamber tubenear the temperature sensor 28B. Of course, temperature sensor 28A,temperature sensor 28B, and/or other temperature sensors can be placedanywhere near the likely formation of reductant deposits.

Positioning temperature sensors (e.g., temperature sensors 28A, 28B) atlocations (such as shown in FIG. 3) near likely reductant deposit sitesmay provide the benefit of exposing the temperature sensors to arelatively large temperature variation that occurs with development ofan associated reductant deposit (e.g., reductant deposits 74A, 74B).With regard to the likely formation of reductant deposit 74A in thelocation shown, during normal operation of the SCR system 18, eddycurrents in the mixture of exhaust gas and reductant 38 may developwithin the boss 70. Such eddy currents may contain heated gases movingat a relatively high velocity that therefore transmit considerable heatto any structures within the exhaust line 24, the exhaust line 24itself, and the exterior wall 69. The presence of a reductant depositsuch as the reductant deposits 74A, 74B may impede the flow of theseeddy currents, thereby impeding the associated heat transfer to reducethe temperature of structures within the exhaust line 24, the exhaustline 24 itself, and the exterior wall 69.

Thus, the location of the temperature sensors 28A, 28B shown in FIG. 3may be beneficial because the temperature sensors 28A, 28B may bepositioned within or near where these eddy currents normally develop.The temperature sensor 28A may, in its entirety, be positioned in theboss 70 as shown. Alternatively, the temperature sensor 28A may beinserted through a small opening (not shown) in the exterior wall 69 orthe wall of the boss 70 so that the sensing portion of the temperaturesensor 28A is positioned within the boss 70. The temperature sensor 28Bmay, in its entirety, be positioned in the sidewall (e.g., exterior wall69) of the exhaust line 24 as shown. Alternatively, the temperaturesensor 28B may be inserted through a small opening (not shown) in theexterior wall 69 of the exhaust line 24 so that the sensing portion ofthe temperature sensor 28B is positioned within the exhaust line. Thetemperature sensors 28A, 28B may be any type of temperature sensorsknown in the art, including thermocouples, resistance temperaturedetectors (RTDs), thermistors, and the like.

Temperature sensors may alternatively be positioned at a wide variety oflocations, either within the boss 70, within the reaction chamber 22, orwithin the exhaust line 24 proximate or downstream of the boss 70. Asanother alternative, the temperature sensor 28 may be positioned outsidethe exhaust line 24, the reaction chamber 22, and/or the boss 70. Atsuch a location, the temperature sensor 28 may effectively measure heattransfer through the exterior wall 69 and/or the wall of the boss 70.The speed at which heated gas flows through the exhaust line 24, thereaction chamber 22, and/or the boss 70 may control heat transferthrough these structures, so positioning the temperature sensor 28outside the flow of gas may provide sufficient data to determine whethera reductant deposit has formed.

Referring to FIG. 4, a chart 80 illustrates how temperature data maychange over time as a reductant deposit builds in the exhaustaftertreatment system such as the SCR system 18 of FIG. 1. The chart 80has a horizontal axis 82 that indicates elapsed time, and a verticalaxis 84 that indicates the temperature measured by a temperature sensorsuch as the temperature sensor 28. A temperature line 86 shows how thetemperature may vary over time.

As shown, the temperature line 86 may have multiple regions including anormal temperature region 88, an increased temperature region 89, adecreased temperature region 90, and a low temperature region 91. Thenormal temperature region 88 may represent the performance of the SCRsystem 18 under generally normal conditions, i.e., without a significantreductant deposit.

As a reductant deposit, like the reductant deposits 74A, 74B begins toform, it may cause a short-term increase in temperature as indicated bythe increased temperature region 89. The brief increase in exhausttemperature may be caused by a temporary increase in the velocity ofeddy currents or other gas flow and/or heat transfer phenomena near thereductant deposit site. As the reductant deposit grows, the temperaturemay drop for the reasons set forth in the discussion of FIG. 3, thusleading to the reduced temperature region 90 immediately after thetemperature drop, and subsequently, the low temperature region 91 inwhich the temperature remains relatively low (with significantvariation) until the reductant deposit is removed. The variation iscaused by the continual evolution of the formation of the deposit (e.g.,brief periods of incremental build-up between brief periods ofincremental reduction).

The normal temperature region 88 may have a relatively stabletemperature. This temperature may be on the order of 225° C. to 325° C.in some embodiments. The normal temperature region 88 may have avariation 94 between its maximum and minimum temperatures that isrelatively low, for example, only a few degrees Centigrade. Thetemperature may then rise by a temperature increase 95 from the averagetemperature in the normal temperature region 88 to reach the maximumtemperature of the increased temperature region 89.

Alternatively, the temperature may fall as it approaches the increasedtemperature region 89 so that the maximum temperature of the increasedtemperature region 89 is no higher than the average temperature in thenormal temperature region 88. However, in this case, a discernibletemperature increase may still exist during the early stages of depositformation. The temperature increase may define an increased temperatureregion with a sharper increase than the increased temperature region 89of FIG. 4 so as to define a temperature “spike.”

After the increased temperature region 89, the temperature may fall backto the average temperature in the normal temperature region 88, andcontinue to fall by a temperature decrease 96 from the averagetemperature in the normal temperature region 88 to the averagetemperature in the low temperature region 91. The average temperature inthe low temperature region 91 may be on the order of 100° C. to 200° C.in some embodiments. The low temperature region 91 may exhibit avariation 97 in temperature that is relatively large, for example,around 50° C. or even 100° C.

The chart 80 provides a number of different characteristics of thetemperature that can be compared with established thresholds to diagnosethe formation of a reductant deposit within the SCR system 18.Additionally, the OBD system 40 need not sample a continuous stream oftemperature data; rather, sampling two temperature data points may besufficient. For example, the OBD system 40 may simply compare a firsttemperature sampled from within the normal temperature region 88 with asecond temperature sampled from within the low temperature region 91. Ifthe temperature differential (i.e., the temperature drop) between thefirst and second temperatures exceeds a threshold temperaturedifferential, the OBD system 40 may determine that a reductant depositexists within the SCR system 18. This method will be shown and describedin connection with FIG. 5.

Referring to FIG. 5, a flow chart diagram illustrates a method 100 fordiagnosing and/or responding to the existence of a reductant deposit inthe SCR system 18 of FIG. 1, according to one embodiment of theinvention. The method 100 may operate continuously, or may be triggeredby one or more events such as the passage of a certain time incrementsince the last time the method 100 was carried out, the previousdetection of a reductant deposit, the previous initiation of aregeneration cycle, the presence of certain loading or operatingconditions of the internal combustion engine 20, or other conditionsinvolved in the operation of the system 10.

As shown, the method may start 110 with a step 120 in which the internalcombustion engine 20 is operated to begin producing exhaust. In a step130, the reductant 38 may be delivered to the exhaust stream. In a step140, the sampling module 58 may be used to sample a first temperature ofthe mixture of exhaust and reductant from the temperature sensor 28. Thefirst temperature may be sampled during the normal temperature region 88of the temperature line 86. In a step 150, the OBD system 40 may waitfor a given time increment such as, for example, the time required forthe temperature to progress from the normal temperature region 88 ofFIG. 4 to the decreased temperature region 90 or the low temperatureregion 91 of FIG. 4 if a reductant deposit is forming. However, if thetemperature sampling is continuous, the step 150 may be omitted.

Once the desired time increment has passed, the sampling module 58 maysample a second temperature of the mixture of exhaust and reductant fromthe temperature sensor 28. The second temperature may be sampled duringthe low temperature region 91 of the temperature line 86. Then, in astep 170, the calculation module 60 may calculate the temperaturedifferential between the first and second temperatures sampled in thestep 140 and the step 160. This may be accomplished by subtracting thefirst temperature from the second temperature. Then, in a step 180, thecomparison module 62 may compare the temperature differential with athreshold temperature differential.

In a query 190, if the temperature differential does not exceed thethreshold temperature differential, the method 100 may progress to astep 192 in which the reporting module 64 generates the performancestatus 52 indicating that there is no significant reductant deposit. Themethod 100 may then restart, either immediately or after a desired timeincrement has passed.

If the temperature differential does exceed the threshold temperaturedifferential, the method 100 may progress to a step 194 in which thereporting module 64 generates the performance status 52 indicating thata significant reductant deposit does exist. If desired, in a step 196, aregeneration cycle may then be initiated to automatically regenerate theSCR system 18 to clear the reductant deposit.

According to one example, regeneration may be accomplished bytransmitting the performance status 52 to the controller 42 so that thecontroller 42 can automatically initiate the desired remedial measures.The control module 66 may issue the command 56 to the reductant deliverysystem 30 to alter the operation of the reductant delivery system 30 tofacilitate removal of the reductant deposit, for example, by stoppingthe flow of the reductant 38 through the injector 36. The regenerationmodule 68 may similarly issue the command 54 to the internal combustionengine 20 to alter the operation of the internal combustion engine 20 tofurther help remove the reductant deposit. For example, the command 54may cause the internal combustion engine 20 to run at a highertemperature, thereby increasing the temperature of the exhaust streamflowing through the exhaust line 24 to a temperature that breaks down,burns, and/or otherwise removes the reductant deposit.

After the regeneration cycle has been completed, the method 100 may thenrestart, either immediately or after a desired time increment haspassed. It may be desirable to restart the method 100 immediately aftercompletion of the step 196 to ensure that the reductant deposit has beensuccessfully removed. Alternatively, a modified method may be used afterthe performance of the step 196. For example, only a single temperature(e.g., a third temperature) may need to be sampled. The thirdtemperature may be compared with the first temperature and/or the secondtemperature to rapidly determine whether the SCR system 18 has returnedto normal operating conditions.

In the alternative to the foregoing method, the OBD system 40 may usedifferent methods to diagnose the existence of a reductant deposit. Forexample, the OBD system 40 may instead calculate the temperaturedifferential between a first temperature within the normal temperatureregion 88 and a second temperature within the increased temperatureregion 89. The resulting temperature differential may then be atemperature rise. In other alternatives, the OBD system 40 may calculatethe temperature differential between a first temperature within thenormal temperature region 88 or within the increased temperature region89 and a second temperature within the decreased temperature region 90.Again, the temperature differential may be a temperature drop.

In any of the foregoing cases, the elapsed time between measurement ofthe first and second temperatures may be determined from observation ofexperimental data, i.e., how long the SCR system 18 takes, duringformation of a reductant deposit, to go from the normal temperatureregion 88 to the increased temperature region 89, the decreasedtemperature region 90, or the low temperature region 91, or from theincreased temperature region 89 to the decreased temperature region 90or low temperature region 91, etc. A simple comparison of twotemperature data points can be made as set forth above or, if desired,additional temperature data points may be collected and analyzed toprovide a more complete and/or reliable diagnosis.

In the alternative to looking for a temperature drop or a temperaturerise, the OBD system 40 may instead look for a change in othercharacteristics of the temperature data. In one embodiment, the OBDsystem 40 analyzes the temperature data to look for the amplitude ofvariations in the temperature over time. For example, the OBD system 40may sample temperature data and, based on a standard deviation or othermeasurement of variation of the data, determine whether a reductantdeposit exists. If the variation in temperature data is like thevariation 94 in FIG. 4, the OBD system 40 may conclude that there is nosignificant reductant deposit in the SCR system 18. Conversely, if thevariation in temperature data is like the variation 97 in FIG. 4, theOBD system 40 may conclude that a reductant deposit exists in the SCRsystem 18.

If the OBD system 40 is measuring temperature amplitude instead of atemperature drop or temperature rise, the calculation module 60 maydetermine an absolute value of the difference between the first andsecond temperatures. The comparison module 62 may then compare thisabsolute value to a threshold temperature differential that acts as athreshold amplitude. If the absolute value of the difference is greaterthan the threshold amplitude, the reporting module 64 may issue theperformance status 52 indicating that there is a reductant deposit. Ifthe absolute value of the difference is not greater than the thresholdamplitude, the reporting module 64 may issue the performance status 52indicating that there is no reductant deposit.

As another alternative to the method 100 of FIG. 5, a different OBDsystem (not shown) may only sample a single temperature from a singletemperature sensor like the temperature sensor 28. If the singletemperature is, for example, below a given temperature threshold, theOBD system may then determine that a reductant deposit has formed. Forexample, if the steady-state temperature of the exhaust aftertreatmentsystem is 225° C. to 325° C., the OBD system may determine that thereductant deposit exists if the temperature reading is below 225° C.Other temperatures may, of course, be used for the threshold, such as125° C., 150° C., 175° C., or 200° C.

As yet another alternative, a different OBD system (not shown) may onlysample a single temperature from a single temperature sensor like thetemperature sensor 28. If the single temperature is, for example, abovea given temperature threshold, the OBD system may then determine that areductant deposit has formed. For example, if the steady-statetemperature of the exhaust aftertreatment system is 225° C. to 325° C.,the OBD system may determine that the reductant deposit exists if thetemperature reading is greater than 325° C. Other temperatures may, ofcourse, be used for the threshold, such as 350° C. or 375° C. Such amethod makes use of the temperature “spike” that may be observed uponinitial formation of the reductant deposit.

The chart 80 is merely exemplary and represents how the data from onelocation of the temperature sensor 28 might appear. The manner in whichthe temperature responds to reductant deposit formation will bedifferent for each temperature sensor location. Similarly, the manner inwhich the deposit formation is diagnosed by the OBD system 40 may bedifferent from the methods set forth above. A wide variety oftemperature phenomena may occur over time with different sensorplacements; the present invention contemplates all methods utilizing anysuch phenomena to diagnose the existence of a reductant deposit in anexhaust aftertreatment system.

If desired, multiple temperature sensors (not shown) may be used toprovide multiple sources of temperature data for more accuratediagnosis. If multiple sensors are used, the comparison module 62 may beused to compare data from multiple sensors, in place of or in additionto the comparison of data from a single sensor taken at different pointsin time. For example, in addition to the temperature sensor 28, anadditional temperature sensor may be placed upstream of the boss 70, andthe temperature drop from the upstream sensor to the temperature sensor28 may be calculated and compared with pre-existing thresholds todetermine whether an obstruction such as the reductant deposit 74 isproducing a larger-than-expected temperature drop.

As another alternative, other types of sensors may be used incombination with the temperature sensor 28. For example, one or morepressure sensors may be positioned in the exhaust line 24, the reactionchamber 22, and/or the boss 70 to measure the pressure drop occurringwithin one or more of these components. Such information may help todetermine whether the temperature data 50 truly indicates the presenceof a reductant deposit, or are indicative of a different anomaly withinthe SCR system 18. For example, the temperature of the mixture ofexhaust and reductant 38 may also be affected by the pressure of themixture, which may in turn be affected by factors such as the dosingrate of the reductant 38 and the loading of the internal combustionengine 20. Thus, the comparison module 62 may reference not just onethreshold temperature differential, but may have an array of thresholdtemperature differentials that apply to different operating conditionsof the system 10 and/or to different pressures of the mixture of exhaustand reductant 38.

According to one example, each range of pressure drops within theexhaust line 24 may have a different threshold temperature differentialthat applies to it. Thus, the sampling module 58 may sample pressuredata (not shown) in addition to the temperature data 50. The calculationmodule 60 may calculate a pressure drop, or “pressure differential” inaddition to the temperature differential. The comparison module 62 maythen reference an array of pressure differential ranges to find therange within which the measured pressure differential falls, and thenlocate the applicable threshold temperature differential. This thresholdtemperature differential may then be used by the comparison module 62 todetermine whether a reductant deposit is present within the SCR system18.

The schematic flow chart diagrams and method schematic diagramsdescribed above are generally set forth as logical flow chart diagrams.As such, the depicted order and labeled steps are indicative ofrepresentative embodiments. Other steps, orderings and methods may beconceived that are equivalent in function, logic, or effect to one ormore steps, or portions thereof, of the methods illustrated in theschematic diagrams.

Additionally, the format and symbols employed are provided to explainthe logical steps of the schematic diagrams and are understood not tolimit the scope of the methods illustrated by the diagrams. Althoughvarious arrow types and line types may be employed in the schematicdiagrams, they are understood not to limit the scope of thecorresponding methods. Indeed, some arrows or other connectors may beused to indicate only the logical flow of a method. For instance, anarrow may indicate a waiting or monitoring period of unspecifiedduration between enumerated steps of a depicted method. Additionally,the order in which a particular method occurs may or may not strictlyadhere to the order of the corresponding steps shown.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of computer readable program code may be a singleinstruction, or many instructions, and may even be distributed overseveral different code segments, among different programs, and acrossseveral memory devices. Similarly, operational data may be identifiedand illustrated herein within modules, and may be embodied in anysuitable form and organized within any suitable type of data structure.The operational data may be collected as a single data set, or may bedistributed over different locations including over different storagedevices, and may exist, at least partially, merely as electronic signalson a system or network. Where a module or portions of a module areimplemented in software, the computer readable program code may bestored and/or propagated on in one or more computer readable medium(s).

The computer readable medium may be a tangible computer readable storagemedium storing the computer readable program code. The computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, holographic,micromechanical, or semiconductor system, apparatus, or device, or anysuitable combination of the foregoing.

More specific examples of the computer readable medium may include butare not limited to a portable computer diskette, a hard disk, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), a portable compact discread-only memory (CD-ROM), a digital versatile disc (DVD), an opticalstorage device, a magnetic storage device, a holographic storage medium,a micromechanical storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, and/or storecomputer readable program code for use by and/or in connection with aninstruction execution system, apparatus, or device.

The computer readable medium may also be a computer readable signalmedium. A computer readable signal medium may include a propagated datasignal with computer readable program code embodied therein, forexample, in baseband or as part of a carrier wave. Such a propagatedsignal may take any of a variety of forms, including, but not limitedto, electrical, electro-magnetic, magnetic, optical, or any suitablecombination thereof. A computer readable signal medium may be anycomputer readable medium that is not a computer readable storage mediumand that can communicate, propagate, or transport computer readableprogram code for use by or in connection with an instruction executionsystem, apparatus, or device. Computer readable program code embodied ona computer readable signal medium may be transmitted using anyappropriate medium, including but not limited to wireless, wireline,optical fiber cable, Radio Frequency (RF), or the like, or any suitablecombination of the foregoing

In one embodiment, the computer readable medium may comprise acombination of one or more computer readable storage mediums and one ormore computer readable signal mediums. For example, computer readableprogram code may be both propagated as an electro-magnetic signalthrough a fiber optic cable for execution by a processor and stored onRAM storage device for execution by the processor.

Computer readable program code for carrying out operations for aspectsof the present invention may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The computer readable program code mayexecute entirely on the user's computer, partly on the user's computer,as a stand-alone software package, partly on the user's computer andpartly on a remote computer or entirely on the remote computer orserver. In the latter scenario, the remote computer may be connected tothe user's computer through any type of network, including a local areanetwork (LAN) or a wide area network (WAN), or the connection may bemade to an external computer (for example, through the Internet using anInternet Service Provider).

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment. Similarly, the use of theterm “implementation” means an implementation having a particularfeature, structure, or characteristic described in connection with oneor more embodiments of the present disclosure, however, absent anexpress correlation to indicate otherwise, an implementation may beassociated with one or more embodiments.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the disclosure is, therefore,indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. An apparatus for diagnosing existence ofreductant deposits in an exhaust aftertreatment system having areductant delivery system that delivers reductant to exhaust gasproduced by an internal combustion engine to provide a mixture ofexhaust gas and reductant, and a control module that operates thereductant delivery system, the apparatus comprising: a sampling modulethat samples a first temperature of the mixture of exhaust gas andreductant and samples a second temperature of the mixture of exhaust gasand reductant; a calculation module that calculates a temperaturedifferential between the first and second temperatures; and a comparisonmodule that compares the first temperature differential with a thresholdtemperature differential to determine whether a reductant deposit existswithin the exhaust aftertreatment system.
 2. The apparatus of claim 1,further comprising a reporting module that reports a performance statusindicating existence of a reductant deposit within the exhaustaftertreatment system.
 3. The apparatus of claim 2, further comprising aregeneration module that receives the performance status and, inresponse to receipt of the performance status, initiates a regenerationcycle of the exhaust aftertreatment system to at least partially removethe reductant deposit.
 4. The apparatus of claim 1, wherein the samplingmodule obtains the first and second temperatures from a temperaturesensor positioned in a boss that extends from a decomposition chamber ofthe exhaust aftertreatment system, wherein the reductant delivery systemdelivers the reductant to the exhaust gas through the boss.
 5. Theapparatus of claim 1, wherein the sampling module obtains the first andsecond temperatures from a temperature sensor positioned in or near theexhaust aftertreatment system, wherein, after sampling the firsttemperature, the sampling module waits for a time increment sufficientfor the reductant deposit to form or increase significantly in sizeafter sampling the first temperature.
 6. The apparatus of claim 5,wherein the threshold temperature differential comprises a temperaturerise from the first temperature to the second temperature, wherein thecomparison module determines that the reductant deposit exists if thesecond temperature exceeds the first temperature by an amount greaterthan the temperature rise.
 7. The apparatus of claim 5, wherein thethreshold temperature differential comprises a temperature drop from thefirst temperature to the second temperature, wherein the comparisonmodule determines that the reductant deposit exists if the firsttemperature exceeds the second temperature by an amount greater than thetemperature drop.
 8. The apparatus of claim 5, wherein the thresholdtemperature differential comprises a magnitude of temperature variation;wherein the comparison module determines that the reductant depositexists if the absolute value of the difference between the first andsecond temperatures is greater than the magnitude of temperaturevariation.
 9. The apparatus of claim 1, wherein the sampling modulefurther takes a plurality of temperature samples to obtain at least oneof the first and second temperatures, wherein at least one of the firstand second temperatures comprises an average temperature of theplurality of temperature samples.
 10. A method for diagnosing existenceof a reductant deposit in an exhaust aftertreatment system that deliversreductant to exhaust gas produced by an internal combustion engine toprovide a mixture of exhaust gas and reductant, the method comprising:positioning a temperature sensor in or near the exhaust aftertreatmentsystem; sampling a first temperature of the mixture of exhaust gas andreductant with the temperature sensor; and using the first temperatureto make a comparison to determine whether a reductant deposit has formedin the exhaust aftertreatment system.
 11. The method of claim 10,further comprising: reporting a performance status that the reductantdeposit exists within the exhaust aftertreatment system; and initiatinga regeneration cycle of the internal combustion engine to at leastpartially remove the reductant deposit in response to receipt of theperformance status.
 12. The method of claim 10, further comprising:waiting for a time increment sufficient for the reductant deposit toform or increase significantly in size after sampling the firsttemperature; sampling a second temperature of the mixture of exhaust gasand reductant with the temperature sensor after waiting for the timeincrement; and calculating a temperature differential between the firstand second temperatures.
 13. The method of claim 12, wherein thetemperature sensor is positioned in a boss that extends from adecomposition chamber of the exhaust aftertreatment system, whereindelivering reductant to the exhaust gas comprises delivering thereductant through the boss.
 14. The method of claim 12, wherein thethreshold temperature differential comprises a temperature rise from thefirst temperature to the second temperature, wherein comparing thetemperature differential with the threshold temperature differentialcomprises determining that the reductant deposit exists if the secondtemperature deposit exists by an amount greater than the temperaturerise.
 15. The method of claim 12, wherein the threshold temperaturedifferential comprises a temperature drop occurring from the firsttemperature to the second temperature, wherein comparing the temperaturedifferential with the threshold temperature differential comprisesdetermining that the reductant deposit exists if first temperatureexceeds the second temperature by an amount greater than the temperaturedrop.
 16. The method of claim 12, wherein the threshold temperaturecomprises a magnitude of temperature variation, wherein comparing thetemperature differential with a threshold temperature differentialcomprises determining that the reductant deposit exists if the absolutevalue of the difference between the first and second temperatures isgreater than the magnitude of temperature variation.
 17. The method ofclaim 10, wherein at least one of sampling the first temperature andsampling the second temperature comprises taking a plurality oftemperature samples, wherein at least one of the first temperature andthe second temperature comprises an average temperature of the pluralityof temperature samples.
 18. An internal combustion engine system,comprising: an internal combustion engine; an exhaust aftertreatmentsystem in exhaust gas receiving communication with the internalcombustion engine; a reductant delivery system in reductant supplyingcommunication with exhaust gas in the exhaust aftertreatment system toprovide a mixture of exhaust gas and reductant; a temperature sensorpositioned to measure temperature of the mixture of exhaust gas andreductant; and an on-board diagnostic system that samples temperaturedata from the temperature sensor and uses the temperature data todetermine whether a reductant deposit exists within the exhaustaftertreatment system.
 19. The internal combustion engine system ofclaim 18, wherein sampling temperature data from the temperature sensorcomprises obtaining a first temperature and a second temperature fromthe temperature sensor, wherein the on-board diagnostic furthercalculates a temperature differential between the first and secondtemperatures to provide a first temperature differential, and comparesthe first temperature differential with a threshold temperaturedifferential to determine whether a reductant deposit has formed in theexhaust aftertreatment system.
 20. The internal combustion engine systemof claim 18, wherein the temperature sensor is positioned in a boss thatextends from a decomposition chamber of the exhaust aftertreatmentsystem, wherein the reductant delivery system delivers the reductant tothe exhaust gas through the boss.